LaserBeamsBarrel.cc

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#include "Alignment/LaserAlignmentSimulation/interface/LaserBeamsBarrel.h"

#include "FWCore/MessageLogger/interface/MessageLogger.h"
#include "FWCore/ServiceRegistry/interface/Service.h"
#include "FWCore/Utilities/interface/RandomNumberGenerator.h"

#include "CLHEP/Random/RandGaussQ.h"
#include "globals.hh"                        // Global Constants and typedefs
#include "G4ParticleDefinition.hh"
#include "G4ParticleGun.hh"
#include "G4SystemOfUnits.hh"

LaserBeamsBarrel::LaserBeamsBarrel() :
  theParticleGun(nullptr),
  theDRand48Engine(nullptr)
{
  G4int nPhotonsGun = 1;
  G4int nPhotonsBeam = 1;
  G4double Energy = 1.15 * eV;
  // call constructor with options
  LaserBeamsBarrel(nPhotonsGun, nPhotonsBeam, Energy);
}

LaserBeamsBarrel::LaserBeamsBarrel(G4int nPhotonsInGun, G4int nPhotonsInBeam, G4double PhotonEnergy) : thenParticleInGun(0),
                                                       thenParticle(0),
                                                       thePhotonEnergy(0),
                                                       theParticleGun(),
                                                       theDRand48Engine()
{
  /* *********************************************************************** */
  /*  initialize and configure the particle gun                              */
  /* *********************************************************************** */

  // the Photon energy
  thePhotonEnergy = PhotonEnergy;

  // number of particles in the Laser beam
  thenParticleInGun = nPhotonsInGun;

  // number of particles in one beam. ATTENTION: each beam contains nParticleInGun with the same
  // startpoint and direction. nParticle gives the number of particles in the beam with a different
  // startpoint. They are used to simulate the gaussian beamprofile of the Laser Beams.
  thenParticle = nPhotonsInBeam;

  // create the particle gun
  theParticleGun = new G4ParticleGun(thenParticleInGun);

  // default kinematics
  G4ParticleTable * theParticleTable = G4ParticleTable::GetParticleTable();
  G4ParticleDefinition * theOpticalPhoton = theParticleTable->FindParticle("opticalphoton");

  theParticleGun->SetParticleDefinition(theOpticalPhoton);
  theParticleGun->SetParticleTime(0.0 * ns);
  theParticleGun->SetParticlePosition(G4ThreeVector(-500.0 * cm, 0.0 * cm, 0.0 * cm));
  theParticleGun->SetParticleMomentumDirection(G4ThreeVector(5.0, 3.0, 0.0));
  theParticleGun->SetParticleEnergy(10.0 * keV);
  setOptPhotonPolar(90.0);

  // initialize the random number engine
  theDRand48Engine = new CLHEP::DRand48Engine();

}

LaserBeamsBarrel::~LaserBeamsBarrel()
{
  if ( theParticleGun != nullptr ) { delete theParticleGun; }
  if ( theDRand48Engine != nullptr ) { delete theDRand48Engine; }
}

void LaserBeamsBarrel::GeneratePrimaries(G4Event * myEvent)
{
  // this function is called at the beginning of an Event in LaserAlignment::upDate(const BeginOfEvent * myEvent)

  // use the random number generator service of the framework
  edm::Service<edm::RandomNumberGenerator> rng;
  unsigned int seed = rng->mySeed();

  // set the seed
  theDRand48Engine->setSeed(seed);

  // number of LaserBeams
  const G4int nLaserBeams = 8;

  // z position of the Laserdiodes (value from design drawings)
  G4double LaserPositionZ = 1137.0 * mm; 

  // Radius of the Laser ring
  G4double LaserRingRadius = 564.0 * mm;

  // phi positions of the Laserdiodes (from CMS Note 2001/053 or from http://abbaneo.home.cern.ch/abbaneo/cms/layout)
  G4double LaserPhi[nLaserBeams] = { G4double(7.0/112.0)   * G4double(2.0 * M_PI),
                     G4double(23.0/112.0)  * G4double(2.0 * M_PI),
                     G4double(33.0/112.0)  * G4double(2.0 * M_PI),
                     G4double(49.0/112.0)  * G4double(2.0 * M_PI),
                     G4double(65.0/112.0)  * G4double(2.0 * M_PI),
                     G4double(77.0/112.0)  * G4double(2.0 * M_PI),
                     G4double(93.0/112.0)  * G4double(2.0 * M_PI),
                     G4double(103.0/112.0) * G4double(2.0 * M_PI) };

  // width of the LaserBeams
  G4double LaserBeamSigmaX = 0.5 * mm;
  G4double LaserBeamSigmaY = 0.5 * mm;

  // get the definition of the optical photon
  G4ParticleTable * theParticleTable = G4ParticleTable::GetParticleTable();
  G4ParticleDefinition * theOpticalPhoton = theParticleTable->FindParticle("opticalphoton");

  // loop over the LaserBeams
  for (int theBeam = 0; theBeam < nLaserBeams; theBeam++)
    {
      // code for forward and backward beam
      // calculate x and y position of the current laser diode
      G4double LaserPositionX = cos(LaserPhi[theBeam]) * LaserRingRadius;
      G4double LaserPositionY = sin(LaserPhi[theBeam]) * LaserRingRadius;

      // loop over all the particles in one beam
      for (int theParticle = 0; theParticle < thenParticle; theParticle++)
    {
      // get randomnumbers  and calculate the position
      CLHEP::RandGaussQ aGaussObjX( *theDRand48Engine, LaserPositionX, LaserBeamSigmaX );
      CLHEP::RandGaussQ aGaussObjY( *theDRand48Engine, LaserPositionY, LaserBeamSigmaY );
      
      G4double theXPosition = aGaussObjX.fire();
      G4double theYPosition = aGaussObjY.fire();
      G4double theZPosition = LaserPositionZ;

      // set the properties of the newly created particle
      theParticleGun->SetParticleDefinition(theOpticalPhoton);
      theParticleGun->SetParticleTime(0.0 * ns);
      theParticleGun->SetParticlePosition(G4ThreeVector(theXPosition, theYPosition, theZPosition));
      theParticleGun->SetParticleEnergy(thePhotonEnergy);

      // loop over both directions of the beam
      for (int theDirection = 0; theDirection < 2; theDirection++)
        {
          // shoot in both beam directions ...
          if (theDirection == 0) // shoot in forward direction (+z)
        {
          theParticleGun->SetParticleMomentumDirection(G4ThreeVector(0.0, 0.0, 1.0));
          // set the polarization
          setOptPhotonPolar(90.0);
          // generate the particle
          theParticleGun->GeneratePrimaryVertex(myEvent);
        }
          else if (theDirection == 1) // shoot in backward direction (-z)
        {
          theParticleGun->SetParticleMomentumDirection(G4ThreeVector(0.0, 0.0, -1.0));
          // set the polarization
          setOptPhotonPolar(90.0);
          // generate the particle
          theParticleGun->GeneratePrimaryVertex(myEvent);
        }
        } // end looop over both beam directions
    } // end looop over particles in beam
    } // end loop over beams
}

void LaserBeamsBarrel::setOptPhotonPolar(G4double Angle)
{
  /* *********************************************************************** */
  /*   to get optical processes working properly, you have to make sure      *
   *   that the photon polarisation is defined.                              */
  /* *********************************************************************** */

  // first check if we have an optical photon
  if ( theParticleGun->GetParticleDefinition()->GetParticleName() != "opticalphoton" )
    { 
      edm::LogWarning("SimLaserAlignment:LaserBeamsBarrel") << "<LaserBeamsBarrel::setOptPhotonPolar()>: WARNING! The ParticleGun is not an optical photon";
      return;
    }

//   G4cout << "  AC1CMS: The ParticleGun is an " << theParticleGun->GetParticleDefinition()->GetParticleName();
  G4ThreeVector normal(1.0, 0.0, 0.0);
  G4ThreeVector kphoton = theParticleGun->GetParticleMomentumDirection();
  G4ThreeVector product = normal.cross(kphoton);
  G4double modul2 = product * product;

  G4ThreeVector e_perpendicular(0.0, 0.0, 1.0);
  
  if ( modul2 > 0.0 ) { e_perpendicular = (1.0 / sqrt(modul2)) * product; }
  
  G4ThreeVector e_parallel = e_perpendicular.cross(kphoton);

  G4ThreeVector polar = cos(Angle) * e_parallel + sin(Angle) * e_perpendicular;
  
//   G4cout << ", the polarization = " << polar << G4endl;
  theParticleGun->SetParticlePolarization(polar);
}